Method of producing furfural



Feb. 13, 1934. s. s. GROTH ET AL METHOD OF PRODUCING FURFURAL Filed Sept. 25, 1930 lli Nouk :k

Patented Feb. 13, 1934 UNITED STATES METHOD 0F PRODUCING FURFURAL Bertil Sixten Groth and Georg Henning Blomqvist, Stockholm, Sweden, assignors to Kemiska Kontrollbyrn Aktiebolag, Stockholm, Sweden,

and Aktiebolaget A. Heyman,

Vargarda,

Sweden, Swedish joint-stock companies Application September 25, 1930,

Serial No.

484,275, and in Sweden April 28, 1930 2 Claims.

The present invention is for improvements in and relating to the production of turfural.

Furfural is produced commercially by distilling pentosan-containing materials, such as husks of oat and rice etc., with water or a solution in water of an acid or acid salts at sufliciently high temperature and pressure, for instance at a temperature of about 160 C., corresponding to a pressure above the atmospheric pressure of 5 6 kg/ cm2. By this treatment the pentosans are hydrolyzed and converted into soluble compounds, pentoses, and the pentoses with the aid of heat and acid give furfural, which is distilled off.

Hitherto it has been thought that in this process the hydrolysis of the pentosans to pentoses and the conversion of the pentoses into furfural had to take place in the same step or operation or practically simultaneously. Tests have, however, shown that this theory is not in agreement with actual facts and the present invention therefore consists in that contrary to the methods hitherto in use the hydrolysis of the pentosans to pentoses and the conversion of the pentoses to furfural takes place in separate steps.

The conditions of temperature and pressure etc., at which the hydrolysis of the pentosans to pentoses as well as the conversion of the pentoses to furfural takes place may therefore according to the pres-ent invention vary for the separate steps and for each step be adapted in the most suitable and economical manner. The hydrolysis of the pentosans to pentoses takes place easily and with sufficient velocity at a temperature of about 100 C. in a solution of suitable acidity; the conversion of the pentoses into furfural on the other hand has been found to take place much slower than the former reaction and to require above all a higher temperature (at the same degree of acidity). Thus at a temperature or" 100 C. the formation of the furfural proceeds very slowly, but if the temperature is raised to about 170 C. the pentoses are rapidly converted into fur'fural. An increase of the acidity has the same effect as an increase of the temperature, i. e. it accelerates the hydrolysis of the pentosans to pentoses as well as the conversion of the pentoses into furfural. Thus by carrying out the hydrolysis of the pentosans to pentoses and the conversion of the pentoses into furfural in separate steps according to the present invention the hydrolysis of the pentosans can be carried out at a comparatively low temperature, for example about -110 C. and without raising the pressure or with only a slight increase of pressure, further diierent degrees of acidity may be used in the separate steps, whereby the operation itself as well as above all the apparatus used will be considerably simplied due to the lower pressure employed and the reduced corrosion at the lower temperature, while at the same time heat is saved. However,

ie acidity of the solution should preferably be such that itsl hydrogen ion concentration corresponds to a pH less than 5.

The conversion of the pentosans into pentoses, i.l e. the production of a pentose-containing solution, may be performed in any suitable manner, but it is preferred to use for this purpose a battery of two or more inter-connected boilers or autoclaves, such as described in the Patent No. 1,946,667 (the co-pending application Serial No. li7690), in which the raw material is lixiviated. Collection (and mixing) of the pentose-containing solution in a separate container before the conversion of the pentoses into furfural further ensures that this conversion and the distilling oii of the furfural takes place under substantially constant conditions.

According to the present invention the conversion of the pentoses into furfural is preferably carried out by continuously passing or pumping the pentose-solution produced in the rst step through a soiperheater, in which the formation of the furfural takes place in a few minutes, preferably at a temperature of about 13G-200 C.

The solvent used for the lixiviation of the pentcse-containing raw material preferably has a hydrogen ion concentration corresponding to a pH which is less than 5.

The invention also comprises apparatuses for the carrying out of the process. According to the invention such an apparatus comprises a liXiviator, for example a battery of boilers or autoclaves, and a superheater connected with this lixiviator.

in the following the invention will be described in detail with reference to the accompanying drawing, but it is evident that modifications of the method as well as of the apparatus used are possible within the limits of the invention.

A battery of autoclaves or closed boilers 1, 2, 3 and 4 are iilled with pentosan-containing vegetable refuse, for example husks of oat. The material rests on the lower strainers 51, 52, 53 and 54 and is kept down by the upper strainers 61, 62, 63, 64.

Water or a weak solution of an acid or an acid substance in water is filled into the boilers, so that the material is saturated therewith, and the boilers are heated under pressure to a temperature in the neighbourhood of the boiling point of the liquid at atmospheric pressure. If an acidcontaining liquid is used for the lixiviation the acid may be added when starting the process either successively or continuously or the whole quantity of acid may be added before the liquid enters the first boiler. The process having commenced the degree of acidity may be corrected by continuous or intermittent addition of acid anywhere in the system. For each l kg. husks about 100 liters of a sulphurie acid having a strength 0.5 normal may be used.

The solvent is supplied through the main conduit 7 from which pipes 81, 82, 83, flbranch olf to the bottom of each boiler. The pentose-containing solutions are discharged from the boilers by means of the pipes 91, 92, 93, 91 leading to the common main pipe 10. The lixiviation takes place in such a manner that the incoming solvent iirst meets a boiler containing nearly completely lixiviated material and the outgoing solution nally passes through a boiler containing fresh or nearly fresh material. For this purpose it is necessary that it should be possible to pass solution from one boiler to another and the supply pipes 81, 82, 83, 84 are therefore by means of pipes 111, 112, 113, 11L connected with each of the discharge pipes 92, 93, 94, 91 as shown in the rawing, valves 121, 122, 123, 124 respectively 131, 132, 133, 134 being provided at the branching oif points. By opening or closing the valves the boilers may be connected up as desired for continuous passing of the liquid through the battery and for filling and emptying the same.

At the bottom of each boiler is provided steam coils 141, 142, 143, 144 for heating the solvent in the different boilers and for covering loss of heat by convection, radiation etc.

The number of boilers may vary but should preferably be at least four. One or two boilers in the battery are always disconnected for the emptying of lixiviated material or for the charging of new material. It is advantageous to use a great number of boilers as in this way the composition of the outgoing finfural-containing solution will be more constant.

The hot solution leaving the boilers by the common main pipe is preferably collected in a Well insulated collecting vat 15, from which it is continuously pumped by means of the force pump 16 through the superheater 17, in which the liquid, for example by means of steam introduced at 18, is rapidly heated to a temperature of 1Y0-180 C. and kept at this temperature for some minutes. A certain part of the pentoses of the solution are thereby decomposed to form a corresponding quantity of furfural.

The reaction cannot very well be pushed to a point Where all pentose is converted into iurfural because in that case the furfural under the action of acid and heat is decomposed into non-desirable products.

The reaction is therefore pushed to a. point Where an economical yield of furfural is obtained. The solution leaving the superheater has a temperature of about 170 C. corresponding to a pressure above the atmospheric pressure of 7 8 lrg/cm2 and contains the best part of the acid added in an unchanged state; its content of urfural is about 1%. It also contains a part of the pentoses obtained from the hue-ks by lixiviation in an unchanged state.

The furfural is then distilled off from the solution in a continuously working column 19 or the like at ordinary pressure (or at increased or reduced pressure).

The solution leaving the superheater 17 having a vapor press re corresponding to a temperature of about 170 C. the pressure must be reduced to atmospheric pressure before the soluf tion is introduced into the column, for example by means of a reducing valve or similar apparatus, or preferably by cooling the solution, for example in a coil 2O in the boiler of the column by means of the solvent running down the column and collecting in, the boiler, from which the furfural has been more or less completely separated (the wash). The cooled solution is thc-n introduced at 21 into the column itself, in which the urfural is driven off by means of steam supplied at 22 and the heat given off by the coil 2), or by means of heat supplied in some other way. The solvent running down the column is heated by contact with the coil and gives off steam, whereby the heat of the solution coming from the superheater is utilized.

The solvent from which the furfural has been separated in the column contains in addition to acid and pentoses a small amount of decomposition products of furfural and pentoses in the form of a flocky sediment. This sediment is preferably removed by filtering in a filter press 23, into which the solvent is pumped by means of the pump 2/1, or by centrifuging. A similar treatment may also be undertaken before the distilling off of the furfural in the column, preferably etween the coil 2G and the inlet 21.

The liquid from which furfural and sediment have been removed will thus contain a part of the non-decomposed pentoses and the greater part of the acid originally added (a small part 105 of the acid has been neutralized by basic coinponents present in the raw material). The hot solution is then preferably returned to the lixiviating battery for the lixiviation or a new quantity of husks. It is then first passed to a heatinsulated collecting vat 25 and then by means of the pump 25 to the lixiviating battery.

In this manner the solvent will circulate subject to certain unavoidable losses through decomposition and the like, While pentoses which 115 for practical reasons have been allowed to remain the solution fithout being converted into furfural are recovered as well as the acid present in the solution. Furthermore, the heat of the solvent is also recovered in this manner.

What we cla-iuris:--

l. Method of producing furfural from pentosan-containing materials, which in a combined sequence steps consists in directly producing a pentose-containing solution by lixiviation of 125 the raw material with an aqueous solution at such a temperature that the pentosans are substantially transformed into pentoses, separating the pentose solution thus obtained from the residues of the raw material, then converting pen- 'w toses in said solution into furfural by heating at a temperature between 130 and 200 centigrade, and nally distilling olf furfural from the furfural solution thus obtained. I

2. Method of producing furfural from penf: tosan-containing materials, which in a combined sequence of steps consists in directly producing a pentose-containing solution by lixiviation of the raw material with a solvent having l, a hydrogen ion concentration corresponding to a *Ap pl-l which is less than 5 at a temperature beween and lli)o centigrade, separating the pentose solution thus obtained from the residues of the raw material, then converting pentoses in said solution into furfural by heating at a tem- 5" f perature between 13G and 186 centigrade, a naliy distiiling oir" furfural from the furfural solution thus obtained.

BERTIL SIXTEN GROTE. ,M GEORG HENNING BLOMQVIST. U" 

